On the origin of pressure and magnetic perturbations ahead of dipolarization fronts

Abstract

Dipolarization fronts (DFs), earthward-propagating structures in the Earth's magnetotail current sheet with sharp enhancements of the northward magnetic field Bz, are typically preceded by minor decreases in Bz. Other characteristic DF precursor signatures, including earthward flows and plasma density/pressure enhancements, have been explained in the context of ion acceleration and reflection at dipolarization fronts. In the same context here we simulate the spatial distribution of plasma pressure earthward of a convex DF. The resultant pressure distribution, which shows clear dawn-dusk asymmetries with greater enhancements at the DF duskside, agrees with statistical observations. The simulation further reveals that the reflected ions can carry a secondary current earthward of the advancing DF, which explains the characteristic signature of the Bz dip immediately ahead of the DF. Key Points Simulate the observed dawn-dusk asymmetric pressure buildup ahead of DFs Reveal the role of DF-reflected ions in generating the Bz dips ahead of DFs Explain the origin of DF precursor signatures in the ion DF-reflection context ©2013. American Geophysical Union. All Rights Reserved.